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LM7171: LM7171

Narendra Kumar91
Prodigy 70 points
Part Number: LM7171

Hello

I rig up simple voltage feedback circuit  using LM7171 OP AMP.  Schematic looks as below.

UUT  = 30V.  with gain of 2.  PIN #3 was floating.   it is found after sometime (15 to 20 seconds), IC is getting hot.  I didn't debug the circuit yet.  

Kindy suggests what would be wrong in the schematic?

Regards

Kumar

  • 0
    TI__Expert 8540 points
    Hi Kumar,

    With pin 3 floating, the amplifier is going to drive into one voltage rail or the other, saturating the output/input. That is likely what is causing the heating you are noticing. I would advise connecting the non-inverting input to mid-supply as a bias point instead of leaving it floating.

    Regards,
  • 0 in reply to Jacob Freet
    Prodigy 70 points

    Hi Jacob,

    UUT =12V, I have connected the Pin#3 to ground for initial conditions. IC is not getting heated.  I feel,12 volts is not issue. still testing with different voltage conditions.

    UUT = 32V, even input Is connected ground, still IC is getting HOT. Not sure what will be the reason.

    Output is not connected to any load. still IC is getting HOT. what could be the reason?

    voltage range on the Pin #3 is 1.5 to 5V. with gain of 3 V.

    Regards

    Kumar

  • 0 in reply to Narendra Kumar91
    Guru 140200 points
    Hi Narendra,

    you wire this OPAmp totally atypically! You must not connect the +input to the negative rail (0V) but must stay away from it 1.7...1.8V (typically). If you connect the +input to 0V the output of OPAmp can swing to the positive rail. This can result in a differential input voltage exceeding the maximum rating of +/-10V. By this you barbecue the OPAmp!

    Kai